Jim Grant's Tech Tips
'99 Ford Expedition, Out of Control Idle
What would cause a '99 Ford Expedition to go up to 1500 RPM when starting and then when it should drop back down to 850 or so RPM it will stall instead, unless I keep my foot on the gas. But, when it warms up you will hear the idle go up a little and you can slowly let off and the idle is fine. The problem does not occur when the temperature is warm outside?
Whenever there is an idle control problem I suggest checking the throttle plates for carbon deposits and checking what is called the minimum idle speed. Deposits on the throttle plates can cause an assortment of idle control issues and the correct minimum idle speed setting is needed for the computer to have a baseline to work from for idle control. If these two services/inspection have been performed and you still have an idle problem the next item to check would be the idle air control motor or auxiliary air valve (both mean the same thing). The idle air control motor is used by the computer to control idle speed of the engine for different conditions and loads. These valves can get wiggy and will cause a wide range of idle issues that will not set a computer code. By the way, if the "Check Engine" light is on you will need to have that addressed before dealing with any idle issue. The computer has to have a clean mind to perform such tasks as idle control.